This application is based upon and claims the benefit of priority from the prior Japanese Patent application No. 11-243856, filed Aug. 30, 1999, the entire contents of which are incorporated herein by reference.
The present invention relates to an X-ray computed tomography apparatus in which an X-ray tube is cooled by coolant, for example oil or cooling water. This will be explained using the most popular oil as an example.
FIG. 1 shows a structure of a rotation section inside a gantry of a conventional X-ray computed tomography apparatus. A substantially annular rotor 77 is rotatably supported by a fixing section (not shown). This rotor 77 has X-ray tube unit 71 and an X-ray detector 76 mounted thereon. This X-ray tube utilizes a braking X-ray that is accelerated by a high voltage applied between a cathode and an anode and generated by causing collision with the anode at a very high speed. As well known, the conversion efficiency of the X-ray energy against electric energy is very low, and 99% or more of the electric energy is converted into a heat. When a focal face of the anode is excessively high, the anode material is fused, and cracks, resulting in shorter service life of the X-ray tube. In order to increase a heat capacity, an apparatus of such type housing an X-ray tube in a container together with insulation oil is mainly used at present. In addition, there is employed an apparatus of such type improving a cooling effect by forcibly circulating oil between the X-ray tube unit 71 and a radiator (core) 73 of a radiator unit 72.
Further, in helical scan which is significantly popular recently, it is required to general an X-ray within a comparatively long time and continuously. In addition, X-ray strength per a unit time is likely to increase in order to suppress lower sensitivity due to a higher rotation speed. In order to process the thus increased heat rate, it is required to provide a fan 74 for forcibly cooling oil. The ventilation capability of this fan 74 is very highly designed based on the maximum heat rate of the X-ray tube simulated under a severe scan condition.
Thus, an excessive cooling state can occur under a normal scan condition. This excessive cooling provides an environment in which arcing is likely to occur with thermal electrons inside of the X-ray tube.
In addition, the fan 74 having its very high cooling capability generates a very large operating noise. This operating noise not only causes discomfort to a patient and an operator, but also interferes voice communication between the patient and the operator.
An object of the present invention is to reduce noise in an X-ray computed tomography apparatus, while ensuring the cooling effect of the X-ray tube.
According to the present invention, this apparatus comprises: a rotor rotated in a predetermined direction; an X-ray tube unit mounted on the rotor; an X-ray detector opposed to the X-ray tube unit to detect X-rays transmitted through a subject; a radiator mounted on the rotor; a circulating system configured to circulate and a fluid between the X-ray tube unit and the radiator. The radiator is disposed in a direction in which the radiator is subjected to the air moved by the rotation of the rotor at its front face.
According to the present invention, when the rotor is rotated, the radiator is subjected to the resultant air at its front face, whereby the fluid can be efficiently cooled. In addition, an air cooling fan is eliminated or the operation frequency of the air cooling fan can be reduced, and thus, noise can be significantly reduced.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.